It is known that magnetic components, such as inductors and transformers have many uses. For example inductors may be used in the fabrication of filters and resonant circuits, or may be used in switched mode power converters to boost or to reduce an input voltage for the generation of a different output voltage. Transformers may be used in the transfer of power or signals from one part of a circuit to another part of a circuit while providing high levels of galvanic isolation.
These components can be fabricated within an integrated circuit environment. For example it is known that spaced apart conductors forming generally “spiral” or approximations of “spiral” shapes can be formed on a semiconductor substrate to form a transformer. Such spaced apart spiral inductors can be placed in a side by side or in a stacked configuration. However the performance of such transformers is generally limited by the magnetic coupling between the “coils” formed by the spiral conductors. The conductors are surrounded by an insulating material, such as polyimide. This provides the necessary insulating properties to prevent the conductors from being in galvanic connection with one another, but from a magnetic coupling point of view is little better than an “air-gap” Such transformers therefore offer low efficiency and consequently relatively poor power transfer between the windings of the transformer.
It has been known, in the field macro scale transformers, that the coupling between the windings of the transformer, for example between primary and secondary windings of the transformer, can be enhanced by the inclusion of a core of suitable material. The core is generally made of ferromagnetic material. Manufacturers of macro-scale transformers quickly realized that solid metallic cores were inefficient because eddy currents were induced in them, giving rise to resistive losses within the transformer. Manufacturers of macro-scale transformers overcame these eddy current losses by providing the core as a laminate structure of relatively thin sheets of ferromagnetic material separated from one another by insulating layers. In general the working frequency of the transformer could be increased by decreasing the thickness of the laminations.